1. Field of the Invention
The present invention generally relates to a method for deflecting a fluid flow using a skirt placed around and extending higher than the exit nozzle of a fluid supply system. The method employs a skirt placed in close proximity to a surface to be impinged by the fluid supply. The skirt controls the fluid providing a desired fluid velocity profile along the impinged surface. The invention relates in particular to cryogenic refrigeration utilizing the cooling effect of Joule-Thomson (isenthalpic) expansion of a high pressure refrigerant gas as it passes through a restricting orifice or expansion nozzle into a lower pressure two-phase (liquid-vapor) reservoir in conjunction with the skirt. The skirt deflection method controls the coolant flow direction as it exits the Joule-Thomson expansion nozzle forcing the coolant to remain in close contact with the cooled surface thereby providing for faster cool down times and more uniform temperatures over the entire cooled surface.
2. Background Art
Joule-Thomson refrigeration systems commonly have a configuration which includes helically tinned tubes wrapped around a mandrel. One end of the tubing opens into a reservoir that retains the liquified coolant in thermal contact with an object or surface to be cooled. Examples of objects or surfaces to be cooled by such a refrigeration system include infrared detectors or cold end plate surfaces bonded to detectors in a thermally conductive manner. Prior art Joule-Thomson coolers have been used for more than 20 years to cool infrared detectors and other temperature sensitive instruments.
Low pressure gas/liquid mixture coolant vaporizes as it cools the object and then flows in a return path along the fins outside the tubing to pre-cool the high pressure gas supply flowing inside the tubes toward the reservoir. Many variations of this configuration have been developed to improve the heat exchange between the supply and return gas and between the reservoir and the object being cooled. Other improvements have been to provide a thermostatically controlled supply gas shut-off valve for conserving the limited supply of coolant, and the use of a thermostatically self-regulating mechanism to automatically adjust the crosssectional area of the valve orifice in response to varying temperature, pressure and heat load to achieve high temperature stability. Examples of refrigeration systems employing this compact configuration are described in U.S. Pat. Nos. 3,942,010 to Peterson et al., 4,647,778 to Kline et al., 4,750,338 to Hingst, 5,077,979 to Skertic et al., 5,119,637 to Bard et al., 5,150,579 to Hingst, and 5,337,572 to Longsworth. None of these systems employ a skirt to obtain faster cool down times and more uniform temperatures over the entire cooled surface.
Several spray deflection systems have been developed. However, these systems typically are used to deflect coating materials or water for cleaning, cooling, irrigation and fire protection. Spray deflection systems used for coating applications and water are described in U.S. Pat. Nos. 4,405,018 to Fischer, and 5,190,222, 5,275,340, and 5,333,794 to Haruch. None of these systems employs spray deflection for enhancement of cryogenic cooling systems.